It is well known to provide an agricultural harvester with a sensor disposed adjacent a crop material feed tube for determining a crop material characteristic such as moisture content as the crop material is being pushed through the tube by an auger. The sensor may be an RF microwave sensor as disclosed by Hamid and Stuchly in the publication IEEE Transactions on Industrial Electronics and Control Instrumentation, Vol. IECI-22, May, 1975, or a capacitance or inductance sensor as disclosed in U.S. Pat. No. 5,092,819 to Schroeder et al. In order to develop an accurate measurement of the crop material moisture content these sensors require a constant packing density of the crop material as it moves through the sensing region. The Schroeder et al. patent teaches that the packing density may be made more uniform by providing an auger having a reduced radial dimension in the sensing region where the sensor senses the crop material. The reduced radial dimension makes the auger less efficient in pushing the crop material through the sensing region. The auger flight section upstream of the sensing region pushes the crop material into the sensing region where it accumulates until the region is full. Thereafter, as more crop material is pushed into the sensing region it forces crop material out of the sensing region and into the flight section downstream of the sensing region. The crop material in the sensing region is thus packed at a more or less uniform density.
The teaching of Schroeder et al. tends to produce a more uniform packing density in the sensing region but it is not suitable for use in RF microwave sensors unless the auger is specially constructed so that the portion extending through the sensing region is made of a material which is transparent to the microwave sensing signal. Otherwise, rotation of the flight in the field of the sensing signal causes a cyclic variation in the sensor output signal which is unrelated to the crop material moisture content.
To avoid the effect of rotation of the auger on the sensor output signal, a broken flight auger may be provided wherein that portion of the flight that would otherwise be located in the sensing region is completely removed from the auger. This leads to a further problem generally referred to as `bridging`. A layer or `bridge` of crop material is formed around the inner periphery of the crop material feed tube between the upstream and downstream sections of the flight. The crop material in this layer moves through the sensing region at a much slower rate than the crop material nearer the center of the crop material feed tube. Thus, a real time indication of the crop material moisture content as sensed by the sensor may not be the same as the moisture content of the crop material entering the sensing region.